Psychophysiological studies of persons with borderline hypertension of hypertensive parents have suggested that exaggerated heart rate (HR) and blood pressure (BP) responses to psychological stress mediated by the sympathetic nervous system (SNS) may contribute to the pathogenesis of hypertension. SNS-mediated HR and BP responses have been shown to be evoked by active coping (e.g., shock-avoidance or competitive reaction time tasks) in both animals and humans. Renals physiologists (e.g., Guyton) assert that the final determinant of hypertension is the kidney's long-term failure to reduce the elevated BP through increased water and Na excretion. Recently, our laboratory observed that shock-avoidance tasks induce SNS-mediated water and Na retention due to increased tubular reabsorption in volume-loaded dogs. Proposed studies seek to replicate these results in normotensive humans during more naturalistic competitive tasks after volume-loading by ingestion of water and salt tablets. Effects are expected to be greater among persons who are high HR responders to stress and those with hypertensive parents. Later, studies in first dogs and then humans will attempt to block stress-induced renal changes with drugs or surgery, to determine if the renal nerve, circulating catecholamines, renin-angiotensin, and/or intrarenal alpha or beta-adrenergic receptors mediate these effects. Finally, studies of renal excretion and BP effects of chronic exposure to stressful shock-avoidance tasks in rats genetically predisposed to hypertension are also planned. Another goal of this project is to examine whether strenuous physical exercise may reduce HR and BP response to stress, and thereby possibly diminish the risk of later hypertension. Preliminary studies of normotensive men aged 18=26 indicate that those reporting more hours/week spent on exercise have lower HRs when relaxed and especially during stress than those exercising less, even among those with hypertensive parents. Our initial study is designed to replicate these effects in normotensive adults aged 30-50, obtaining data during both laboratory and real-life stresses. Later, we plan to determine whether direct intervention in the form of aerobic exercises training is effective in reducing stress responses of both young and older adults.